This invention relates generally to a printing unit or processor, such as, an office copier, facsimile or non-impact printer, and more particularly concerns an apparatus for decurling sheet material employed therein.
Generally, electrophotographic printing comprises charging a photoconductive member to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a light image of the original document being reproduced. This records an electrostatic latent image on the photoconductive member which corresponds to the informational areas contained within the original document being reproduced. This records an electrostatic latent image on the photoconductive member which corresponds to the informational areas contained within the original document. The latent image is developed by bringing a developer material into contact therewith. In this way, a powder image is formed on the photoconductive member which is subsequently transferred to a sheet of support material. The sheet of support material is then heated to permanently affix the powder image thereto.
As the sheet of support material passes through the various processing stations in the electrophotographic printing machine, a curl or bend is frequently induced therein. Occasionally, this curl or bend may be inherent in the sheet of support material due to the method of manufacture thereof. It has been found that this curl is variable from sheet to sheet within the stack of sheets utilized in the printing machine. The curling of the sheet of support material causes problems of handling as the sheet is processed in the printing machine. Sheets delivered in a curled condition have a tendency to have their edges out of registration with the aligning mechanisms employed in the printing machine. In addition, curled sheets tend to produce jams or misfeeds within the printing machine. In the past, this problem has been resolved by utilizing bars, rollers or cylinders which engage the sheet material as it passes through the printing machine. Frequently, belts or soft rollers are used in conjunction with a hard penetrating roll to remove the curl in a sheet. However, systems of this type have disadvantages. For example, the size of the decurler is not necessarily consistent with that required in some electrophotographic printing machines. In addition, decurlers of this type generally have a high running torque necessitating significant power inputs to operate successfully. Moreover, on many occasions, in electrophotographic printing, devices previously employed smeared the powder image. Also, a conventional decurler, which most often is of the belt/pinch roll type, has a single paper path, although multiple bending can be set along the paper path, the single path is only effective in reducing paper curls that are primarily in one direction; it is not effective in reducing large curl in the other direction. In other words, if a conventional decurler is designed for flattening dominant TI (toward image) curls, it would not be able to reduce large AI (away from image) curls significantly, and vice versa. For this reason, a single path decurler would fail to decurl thin papers as they exhibit both strong AI and TI curls (depending on which side is on the hot fuser roll) at high moisture content.
Various approaches have been devised to improve sheet decurlers to answer the above-detailed problems. The following disclosures appear relevant:
U.S. Pat. No. 4,077,519; Patentee: Huber; issued Mar. 7, 1978. PA1 U.S. Pat. No. 4,326,915; Patentee: Mutschler, Jr.; issued Apr. 27, 1982. PA1 U.S. Pat. No. 4,360,356; Patentee: Hall; issued Nov. 23, 1982. PA1 U.S. Pat. No. 4,475,896; Patentee: Bains; issued Oct. 9, 1984. PA1 U.S. Pat. No. 4,977,432; Patentee: Coombs et al.; issued Dec. 11, 1990. PA1 U.S. Pat. No. 5,066,984; Patentee: Coombs; issued Nov. 19, 1991.
The pertinent portions of the foregoing disclosures may be summarized as follows:
Huber describes a curl detector and separator wherein a paper sheet is passed through the nip of a rotating roll and charging roll, and thereafter the sheet is stripped from the rotating roll by a vacuum stripper which allows the sheet to pass between the nip of a subsequent transport roll pair.
Mutschler, Jr. discloses a sheet decurler apparatus wherein a sheet is pressed into contact with a rigid arcuate member in at least two regions. The sheet moves about the arcuate member or rod in a curved path to remove curl in the sheet. The sheet is bent in one direction by a first rod and in another direction by a second rod.
Hall discloses an apparatus for removing curl from continuous web material during its travel through engagement bars that can be adjusted to remove AI or TI curl.
Bains describes a curling/decurling mechanism that combines a compliant roller with a soft outer layer in a curling roller to form a penetration nip with the compliant roller. Movable parts are employed to control the angle of sheets as they exit from the nip.
Coombs et al. is directed to a decurling device that includes an arcuate concave guide and a feed roll which causes paper to pass between the guide and the feed roll to decurl the paper. A means is included for selectively laterally offsetting paper driven through the device.
Coombs describes a decurling device that includes an arcuate concave guide and a feed roll which causes paper to pass between the guide and the feed roll to decurl the paper. The space between the guide and the roll is greater than the thickness of the paper and the paper is bent in the direction opposite to its curl as it passes through the arched space.
The present invention aims at providing a rotational decurler designed with the capability of bending sheets in both toward image (TI) and away from image (AI) directions. The bending level in either direction can be adjusted automatically to flatten different levels of incoming sheet curl with different properties.